Vulcanization of rubber compositions



Patented May 10, 1949 VULCANIZATION OF RUBBER COMPOSITIONS Paul J. Flory, Kent, and Norman Rabjohn, Akron,

Ohio, assignors to Wingfoot Corporation,

Akron, Ohio, a corporation of Delaware No Drawing Application January 16, 1946, Serial No. 641,652

Claims.

This invention relates to new methods of curing rubber and more specifically to methods of hardening and insolubilizing rubber without heat, or at temperatures substantially lower than those customarily used.

The purpose of this invention is to provide improved methods of curing or vulcanizing rubber compositions. It is customarily desirable to fabricate rubber by molding or otherwise forming it in the tractable uncured state and subsequently curing the formed article. Where the rubber composition involves perishable structures of paper, wax or certain synthetic resins, so that usual curing temperatures may not be used, this invention finds a valuable application. Further, the carefully controlled operations used in curing rubber necessitate expensive and elaborate installations of furnaces, molds and temperature-measuring instruments. By the practice of this invention, rubber articles may be fabricated in the customary manner and the cure subsequently effected by merely storing the article at room temperature or in a moderately heated storeroom, thus eliminating the necessity for elaborate equipment and avoiding the use of high temperatures. a

This invention is useful in curing all types of rubber, including natural latices and coagula, e; g

those of Hevea, braziliensis, which are capable of further chemical reactions owing to the presence of residual olefinic groupings. The expression a rubber containing residual olefinic groupings, as used herein, also includes synthetic rubbers which are polymers of polyolefines or copolymers of the polyolefines and other polymerizable monomers. Polyolefinessuitable for the preparation of suchrubbers are the conjugated hydrocarbon diolefins and their halogen derivatives, such as butadiene-1,3;isoprene, chloroprene, other alkyl or halogen substituted derivatives of butadiene- 1,3, and higher polyenes, such as t'riolefine hydrocarbons. The polyolefin may be used in very small proportions in the mixture of unpolymerized monomers, for example, 0.5 to 5 per cent, as in Butyl;

rubber, or in larger proportions, such as 50 to 80 per cent, as in Buna N or Buna S synthetic rubbers. The conjugated diolefin may also be used to the extent of 100 per cent of the polymerizable monomer as in polychloroprene or polyisoprene. The diolefin may be copolymerized with any polymerizable mono oleflnic compound with which it is compatible, including styrene, acrylonitrile, vinyl acetate, the alkyl acrylates and the corresponding alpha-alkylor halo-acrylates, vinylidene chloride, isobutylene, alkyl fumarate, alkyl maleate, polymerizable homologues thereof and other polymerizable monomers capable of forming interpolymers with the conjugated diolefins.

-In this specification the term Butyl rubber" is used to refer to the synthetic rubber composition made by the polymerization of small proportions of a conjugated diene hydrocarbon with a substantially larger proportion of an iso-olefine containing a single olefine linkage. The Butyl rubbers are prepared from such proportions of monomers that about 0.25 per cent to 8 per cent of the reacting monomers is the conjugated diolefine. The preferred iso-olefines are isobutylene and its alkyl substituted derivatives while the preferred polyenes are butadiene-1,3, and isoprene. The Butyl rubbers may contain minor proportions of other polymerizable monomers besides the polyenes and the iso-olefines, for example styrene. Butyl rubbers are well known in the rubber industry and widely used in applications where gas impervious compositions are desired.

Buna S and Buna N are commercial synthetic rubbers, the former being a copolymer of to per cent of butadiene-l,3 and 20 to50 per cent of styrene and the latter a copolymer of 50 to 80 per cent of butadiene-1,3 and 20 to-50 per cent of acrylonitrile.

The invention involves mixing the rubber composition with a polyazo ester having the structural formula oxahydrocarbon radical, thiahydrocarbon radical,

or the corresponding haloor nitro-substituted aaaaaio 2-ethoxyethyl, and the 2-isopropoxy-n-propyl, an

alkoxyaryl radical, such as methoxyphenyl and ethoiwnaphthyl radicals, a thiahydrocarbon radical, such .as (C2H5S-C2H4), and the corresponding alkyl-, halo-, and ultra-substituted radicals, such as 2-chloroethyl, 3-bromopropyl, fluoromethyl, parachlorophenyl, meta ethyl phenyl, tolyl, xylyl, 2-nitro-phen oxymethyl, and 2,4-dinitrobenzyl radicals.

The multivalent radical designated as R in the above structural formula may by any alkylene radical, such as ethylene, hexamethylene, decamethylene, and 1,2-propylene radicals, the oxaalkylene radicals such as the radical (C2H4OC2H4) derived from diethylene glycOl, the radical (C2H4OC2H4-OC2H4-) derived from triethylene glycol, and the corresponding thia-alkylene radicals, an arylene radical, such as para-phenylene, and the various naphthylene radicals, a divalent radical having both aryl and aliphatic characteristics, such as tolylene toluylene I xylylene (on, on) diphenylene methane and 2,2 bis(diphenylene) rpropane the oxahydrocarbon and thiahydrocarbon radicals corresponding to the above radicals, the alkyl-, haloand nitro substituted derivatives of any of the above radicals, a radical having a valence.

greater than two, such as glyceryl, pentaerythryl (the quadrivalent radical derived from pentaerythritol and similar aliphatic or aromatic hydrocarbon, thiahydrocarbon, oxahydrocarbon and the corresponding alkyl-, halo-, and nitro-substituted radicals.

The new polyazo esters are prepared by react-. ing a polychlorocarbonate of a polyhydroxy derivative having the desired multivalent' radical of the type above described with an ester of hydrazine monocarboxylio acid wherein the carboxylate radical is linked to the desired monovalent radical of the types described above, and subsequent- 1y reacting the hydrazo ester thereby formed with a suitable oxidizing agent for the purpose of con-- verting it to the corresponding polyazo derivative.

The polychlorocarbonates are prepared by re-- acting any polyhydroxy compound involving the desired polyvalent radical, as above described,

'with phosgene until all of the hydroxyl radicals,

or at least a plurality of the hydroxyl radicals, are substituted with chlorocarbonate radicals The polychlorocarbonates are preferably prepared by adding the polyhydroxy compound gradually to an excess of liquid phosgene while maintaining a temperature below 10 C. for the purpose of removing the heat of reaction, as well as to retain the phosgene in liquid state. It is desirable to surmount the reaction flask with a reflux condenser cooled to the liquefying temperature of phosgene for the purpose of condensing the phosgene gas and returning the same to the reaction vessel. Some of the polychlorocarbonates may be purified by distillation, although many can be satisfactorily purified by washing with water and warming to remove excess phosgene and hydrogen chloride.

The preparation of polychlorocarbonates from polyhydroxy compounds having hydroxyl groups attached directly to aryl rings should be conducted in the presence of a basic reagent, such as a tertiary amine or an oxide, hydroxide or carbonate of an alkali or an alkali earth metal.

The esters of hydrazine monocarboxylic acid may be prepared by reacting hydrazine hydrate with the carbonic acid ester having the monovalent organic radical desired in the final composition. Thus, diphenyl carbonate, diethyl carbonate, dibenzyl carbonate and any other carbonate ester may be reacted with an equal molecular proportion of hydrazine hydrate. The reaction takes place immediately, although generally it is desirable to stir the reaction mass and heat it slightly to complete the reaction. The resulting ester is usually a solid which can be separated from the reaction mass by adding water and subsequently recrystallized from alcohol solutions.

The condensation of the polychlorocarbonate with the esters of hydrazine monocarboxylic acid is conducted in solution in a suitable solvent, such as dioxane, and in the presence of a basic reagent. such as triethylamine. pyridine or other tertiary amine or the oxides, carbonates, or hydroxides of an alkali or an alkali earth metal. The resulting polyhydrazo ester may then be separated by adding water to the reaction mixture and purified by recrystallization from ethyl acetate.

The polyhydrazo esters may then be oxidized to the corresponding polyazocompounds by means of concentrated nitric acid or other oxidizing agents. The oxidation reaction is exothermic but the application of heat may be necessary to start the oxidation. Once the reaction has begun, it soon becomes very vigorous and should be controlled by pouring the reaction mass on ice or into cold water. The resulting polyazo compound can be separated from the cooled reaction mass by extracting with benzene or ether and purified by washing with dilute sodium bicarbonate solu-' tions and with water, followed by drying in the presence of anhydrous sodium sulfate. The solvent may then be removed by evaporation, leaving the substantially pure polyazo compound.

The following are examples of compounds 2,4oo,e1o

which may be used in the practice of this lnvening, cloth, 'paperand metal surfaces or as adhetion: sives in bonding rubber or rubber-coated sur- D th] b H faces. The vulcanizing agents are also useful g yeglebue y g oxya in preparing rubber articles by ge1at1on techu II n g niques or by any other conventional rubber proc- Ci :0 -N=NCO'( H2)ioOCN =N OCzH essing t Diethyleneglycol-bis (phenyl azodicarboxylate) 0 H Glyceryl-tris(benzylazodicarboxylate) Para-phenylene-bis (cyclohexylazo dicarboxylate) O O l i O N=N( JO OCN=N-CO@ Thlodlethylene-bis(gamma-chloropropylazo dicarboxylate) Th new curing agents may be d to cure 0 the surface of molded or shaped rubber articles H by preparing a solution of the polyazo compound Cl CHCHPCH" O C N N C 0 g in benzene, or other solvent for the uncured E I] i rubber, and painting the rubber surface there- 1cmemoH, C ,H with. Thin rubber coatings may .be substantially completely cured by this method due to the penetrating effect of the benzene-which carries the v 0 f 3O polyazo compounds into the interior of the rub- & a her article. This painting technique may also be used to splice parts of uncured rubber by contacting the joined rubber parts at the joint with the solution of polyazo ester and holding the Para xylylene-bis (beta-methoxyetliyl-azo dicarboxylatc) 5 joint in position until the solution penetrates 0 f therubber and the polyazo esters efiect the cure. on o-ozm-o- -ren-d-o-om Further details of the practice of this inven- 'tion are set forth in the following specific ex- 2,2-(p p-di (hydroxyphenyl) propane bls(p-nitro plienyl amples azo dicarboxylate) ester I 0 40 Example 1 II II A cement was prepared by dissolving 5 per- C T cent by weight of natural crude rubber in benzene. Diethylene glycol bis(methyl azodicarbox- CHBCC'H3 ylate) was thereafter added to the benzene so- 0 0 I v lution and dissolved therein to the extent of about 0iNC o -N= 0 1.0 mole percent of the rubber computed as C5Ha. The solution was then spread evenly on a smooth glass surface and dried for 2 hours at In accordance Wlth this Invention any C; The rubber film so obtained was transthetic 11931111111Yubber composition conta'imng parent and colorless and exhibited a tensile residual ethylenic unsaturation ma be mixed strength of 2300 pounds per square inch and an withthe polyazo esters of the type described and elongation of 1000 percent subsequently cured by allowing the compositions to stand at room temperature or by subjecting Example 2 them to slight or moderate temperatures. In h procedure of Example 1' repeated general. e t mp r t s required are Substancept that a copolymer of 95'percent styrene and ia y below those usually us to Cure rubber 5 percent isoprene was used in place of natural omp i i n i e p se o sulfur. or other rubber. The resulting cured film was insoluble conventional vulcanization agents. The curing i benzene, action which proceeds at room temperature will Example 3 be accelerated by slight or moderate heating.

The polyazo esters may be added in any manner customarily used in the rubber industry. For example, the compositions may be added and mixed into the rubber composition on an ordinary roll mill, preferably a cooled mill to pre- A latex of a copolymer of 65 percent butadiene-'1,3 and 35 percent styrene containing 57 percent solids was shaken with 5 percent by Weight of hexamethylene bis(ethyl-azodicarbo'xylate) until a uniformly mixed composition bt Th vent the setting of the composition during the g3: g i g g g gg g ig i gi ggq milling operation. The polyazo esters may also perature for 20 hours. A partial cure was notice- 3; i ig to gg z f to i ge; "o able at that time. The samples were completely r 8 m0 e a ex.may 6 use m a cured by heating at 50 C. for four hours. form for coating operations, manufacture of sponge compositions, or any of the conventional Example 4 methods of using rubber latices. The new cur- A 200 gram sample of Butyl rubber was thoring agents may also be added to solutions of ruboughly mixed with 12 grams of dipropylene bisbers and the cements so prepared used in coat- (ethylazodicarboxylate) on a cold roll mill. One

half of the mixture was milled with an additional 100 grams'of Butyl rubber. The two samples containing respectively approximately 6 and 3 percent of the azo-ester both showed evidence of curing on the mill. Test strips became fully cured in 30 minutes when subjected to a tem- Derature of 250 F.

Example 5 Compound Minutes Hexamethylene glycol bis(ethyl azo dical'boxylate) 65 Dietbylene glycol bis(ethyl azo dicarboxylate) 45 Dccamethylene glycol bis (ethyl azodicarboxylate) 80 Although the invention is described with re- .spect to several specific examples it is not intended that the details thereof shall be construed as limitations on the scope of the invention except to the extent incorporated in the following claims.

We claim:

1. A method of vulcanizing a rubber composition which comprises reacting an unvulcanized rubber containing residual olefinic groupings with a compound having the structural formula in which R. is a monovalent radical of the group in which R is a monovalent radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, thiahydrocarbon radicals, and the corresponding haloand nitro-substituted radicals, R. is a multivalent radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, thiahydrocarbon radicals, and the corresponding nitroand halo-substituted radicals, the oxygen atoms being connected to a carbon atom in R and R, and a: is a small whole number between 2 and 5 inclusive.

3. A vmethod of vulcanizing butadiene-L3- styrene rubber which comprises reacting the unvulcanized rubber with a compound having the structural formula.

o n-[o-tnmrd-o-rv]. in which R is a monovalent radical of the group consisting of hydrocarbon radicals, oxahydrccarbon radicals, thiahydrocarbon radicals, and the corresponding haloand nitro-substituted radicals, R; is a multivalent radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, thiahydrocarbon radicals, and the corresponding nitroand halo-substituted radicals, the oxygen atoms being connected to a carbon atom in R. and R, and a: is a small whole number between 2 and 5 inclusive.

4. A method of vulcanizing butadiene-1,3-

acrylonitrile rubber which comprises reacting the unvulcanized rubber with a compound having the structural formula j 0 o i v a R- 0- N=NC0R in which R is a monovalent radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, .thiahydrocarbon radicals, and the corresponding haloand nitro-substituted radicals, R is a multivalent radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, thiahydrocarbon radicals, and the corresponding nitroand halo-substituted radicals, the oxygen atoms being connected to a carbon atom in R and R; and a: is a small whole number between 2 and 5 inclusive.

5. A method of vulcanizing a rubber composition which comprises mixing an unvulcanized rubber containing residual oleiinic groupings with a compound having the structural formula 0 o R[O-CILIN=N(I.IJO-R'], in which R is a monovalen-t radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, thiahydrocarbon radicals, and the corresponding haloand nitro-substituted radicals, R is a multivalent radical of the group consisting of hydrocarbon radicals, oxahydrocarbon radicals, thiahydrocarbon radicals, and the corresponding nitroand halo-substituted radicals, the oxygen atoms being connected to a carbon atom in R and R, and a: is a small whole number between 2 and 5 inclusive, and heating to effect a vulcanization of the rubber.

PAUL J. FLORY. NORMAN RABJOHN.

REFERENCES CITED UNITED STATES PATENTS Name Date Fisher Aug. 22, 1939 Number 

